1. Field of the Invention
This invention relates to systems, devices, and methods for determining the lithology of a formation and monitoring drilling operations while drilling a borehole. More particularly, this invention relates to systems, devices, and methods that utilize dynamic measurements of selected drilling parameters to determine the lithology of a formation being drilled and to monitor drilling operations.
2. Description of the Related Art
Geologic formations below the surface of the earth may contain reservoirs of oil and gas. Measuring properties of the geologic formations provides information that can be useful for locating the reservoirs of oil and gas. Typically, the oil and gas are retrieved by drilling a borehole into the subsurface of the earth. The borehole also provides access to take measurements of the geologic formations.
One technique for measuring the lithology of a formation is to measure interactions between a drill bit drilling the borehole and the formation. These measurements may be generally referred to as Measurement-While-Drilling (MWD). The measurements are performed using sensors disposed with the drill string attached to the drill bit. The sensors are generally disposed in close proximity to the drill bit. The sensors measure certain dynamic drilling parameters downhole such as weight on bit, torque on bit, rotational speed, bit motion (including acceleration), and bending moments.
The dynamic drilling parameters once obtained may be used to determine a type of lithology. Different types of lithology affect the bit-formation interactions in different ways. By correlating values of the dynamic drilling parameters to the values associated with certain types of lithology, the lithology of the formation being drilled may be determined.
The dynamic drilling parameters may also be used for other purposes such as monitoring drilling operations. Monitoring drilling operations may include diagnosing equipment problems and determining borehole stability.
Data from the sensors can be stored in proximity to the sensors with the drill string or transmitted to the surface for recording and analysis. When the data is stored with the drill string, the data can only be accessed when media storing the data is removed from the drill string. To remove the media requires that the drill string be removed from the borehole. A significant time lag can occur between the time the data was obtained and the time the media is accessed for analysis. When the data is transmitted to the surface, the data may be transmitted via drilling mud pulses. Because of the nature of drilling mud pulses, the data transfer rate may be limited. With both of the above data transfer methods, most of the data processing is performed downhole. The amount of data processing performed downhole can be limited by volume constraints or processor speed.
Therefore, what are needed are techniques to improve data transfer to the surface of the earth when measuring dynamic drilling parameters.